In a conventional test frame the intermediate plate or traverse is formed in its corners with finely machined cylindrical bores receiving the tie rods that extend between a pair of end plates. The intermediate plate can be displaced along the tie rods by threaded spindles to position a workpiece or specimen which is placed under stress either by the spindles or by another device.
It is necessary in such devices, and indeed in all such arrangements as extrusion presses and the like wherein a plate or the like slides along a plurality of tie rods, that the tie rods be perfectly parallel. If they are not, the sliding element will bind and not ride easily since either it will have to deform or have to bend the tie rods slightly. In addition any heating or cooling of the sliding element often will misalign the bores and the tie rods to create such a binding, so that these devices must often be readjusted.